The present invention relates to a motor controller suitable for a motor of an electric vehicle, a geared motor or the like. More particularly, it relates to a motor controller employing commutation sensor signals (hereinafter referred to as CS signals) which indicate a position of a rotor pole of a motor, and this controller drives the motor in a sine wave or performs field weakening control. The motor controller keeps on driving the motor in a stable manner even if the motor changes its speed abruptly.
Recently, efficiency of motors has drawn attention in the market from the view of environment protection due to energy saving. In this climate, induction motors have been replaced with dc motors employing magnets. Among other dc motors, a brushless dc motor using a magnet in the rotor section has become a main stream because it is a maintenance free item.
In order to drive a brushless dc motor efficiently and smoothly, the following control method is employed: A sine wave current-in phase with a back electromotive force produced in a driving coil by magnet-flows through the driving coil, when the motor is driven. In this control method, a position angle of the rotor must be exactly measured. A motor for factory automation and a motor for electric vehicle employ an encoder or a resolver which is widely used as a detector for a rotor position angle. These detectors can produce a resolution of more than 1000 pulses per rotation; however, they are very expensive. On the other hand, a commutation sensor (CS), which detects only a pole position of a rotor magnet, is also used in general. This CS produces a resolution of 12 pulses per rotation in a case of a motor having 4 poles and 3 phases; however, measuring the time between pulses allows the CS to estimate a rotor-position-angle as accurately as the encoder or the resolver measures.
However, in these conventional motor controllers, the following problem occurs when a geared motor, having a gear on an output shaft, encounters a large acceleration or reduction in speed. To be more specific, when the geared motor is in the application where the motor encounters back rush via the gear, or the motor is reversely rotated by external force, the motor produces vibration or cannot be controlled. Because an error of estimating a rotor position angle becomes large, and only a torque smaller than a torque designated can be produced, or current is flowed so that a reversal torque is produced.
The present invention addresses the problem discussed above and aims to provide a motor controller which keeps on driving the motor in a stable manner even when the motor changes its speed abruptly.
The motor controller of the present invention drives a motor based on a commutation sensor signal (CS signal) and comprises the following elements:
(a) a pole position detector for detecting a pole position of a rotor by using edges of CS signals;
(b) a speed detector for detecting a motor speed by using a time interval between edges of the CS signals;
(c) a pole phase detector for estimating a rotor-position-angle based on an output from the speed detector and an output from the pole position detector; and
(d) a phase limiter for restraining an estimated position angle of the rotor from advancing over a predetermined value when the motor reduces its speed abruptly.
This structure allows the motor controller to drive the motor in a stable manner even when the motor reduces its speed abruptly.
Another motor controller of the present invention comprises the following elements:
(a) a pole position detector for detecting a pole position of a rotor by using edges of CS signals;
(b) a speed detector for detecting a motor speed by using a time interval between edges of the CS signals;
(c) a pole phase detector for estimating a rotor-position-angle based on an output from the speed detector and an output from the pole position detector; and
(d) a phase reseter for correcting a deviation of an estimated position angle of the rotor when the motor accelerates its speed abruptly.
This structure allows the motor controller to drive the motor in a stable manner even when the motor accelerates its speed abruptly.
Still another motor controller of the present invention comprises the following elements:
(a) a pole position detector for detecting a pole position of a rotor by using edges of CS signals;
(d) a monitor for recognizing motor""s rotating status by using a pattern of the CS signals; and
(c) a motor drive mode switch for assigning one of a sine wave driving or a rectangular wave driving to the motor, When the monitor recognizes a rotation reverse to the rotation just before, the mode switch changes the sine wave driving to the rectangular wave driving.
This structure allows the motor controller to keep on driving the motor in a stable manner even when a motor speed is abruptly changed by external force, or when a geared motor encounters back rush via the gear provided to an output shaft.